Such a device for producing nonwoven fabric is known from German Auslegeschrift No. DE-AS 19 27 863. In the prior-art nonwoven fabric layering apparatus, there is a problem with web layering in the edge area of the layering width. The lower layering carriage must slow down its travel at these sites, come to a standstill, and then accelerate again in the opposite direction. The web coming from the web producer is, of course, fed to the nonwoven fabric layering apparatus at a constant speed. In the nonwoven fabric layering apparatus, the layering belts run at a constant speed, which causes the web to leave the nonwoven fabric layering apparatus at always the same speed. However, in the edge areas, where the lower layering carriage has a lower speed due to the slowing down, stopping and then accelerating, more web is layered in the outside edges than in other areas of the layering width due to this difference in speed.
A further development of the nonwoven fabric layering apparatus is known from German Patent No. DE-PS 24 29 106. It claims to prevent the edge buildups by having travel movements of the upper carriage and layering carriage being uncoupled from one another and being separately adjustable. Auxiliary carriages are then provided as well in order to compensate for the resulting differences in length of the layering belts. The traveling speeds of the upper carriage, the layering carriage and the auxiliary carriages must then support one another in a certain ratio. This requires a considerable expense for construction and control. Besides, the complicated kinematics impedes the adjusting of different operating conditions of the nonwoven fabric layering apparatus for adaptation to different types of webs or web producers.